P0444

Evaporative Emission Control System Purge Control Valve Circuit Open

Indicator

This indicates that a portion of the EVAP control system is no longer functioning properly. The EVAP system consists of components including (but not limited to) the gas cap, fuel lines, charcoal canister, purge valve, system pressure and flow sensors, electrical wiring and connectors, vacuum lines, the fuel tank, and fuel vapor hoses.

Code Set Parameters

Variations in evaporative emission control system pressure or flow are received by the PCM in degrees of voltage. If the PCM detects a voltage reading that does not coincide with the manufacturer’s reference voltage, a code will be stored and a malfunction indicator will be illuminated. Some models require multiple failure cycles for service engine soon lamp illumination but a code is normally stored on the first failure. Stored codes presented without malfunction indicator lamp illumination may be read as pending codes.

Symptoms

Normally, no symptoms other than a stored code and a service engine soon lamp will be exhibited. However, other evaporative emission control system codes are likely to be present.

Common Causes

These may include a faulty or improperly installed fuel cap, a faulty purge control solenoid, clogged or broken charcoal canister, broken or cracked vacuum or fuel vapor hoses, a faulty pressure or flow sensor, or a bad PCM. PCM failure is rare.

Common Misdiagnosis

Evaporative emission control system components are often replaced in error when a vacuum leak is present or the fuel cap is not properly tightened.

Diagnosis

The evaporative emission control system is responsible for capturing fuel vapors (from the fuel tank and lines) before they escape into the atmosphere

This is usually accomplished using a combination of engine vacuum, a charcoal storage reservoir, and electrically powered solenoids

Flammable fuel vapors are directed to the charcoal canister via plastic or metal hoses where they are stored until a signal from the PCM activates the purge control solenoid

The purge control solenoid opens the purge control valve (with the engine running) and allows engine vacuum to draw the fuel vapors into the engine where they are burned just like liquid fuel.
The charcoal canister is typically located near the fuel tank, which is underneath the vehicle

The fuel vapor and vacuum hoses can be quite long and subject to damage from the elements and road debris.
Several tools may be needed to successfully diagnose this code if no exhaust leaks are detected

A suitable scanner (or code reader), a digital volt/ohmmeter, and a smoke machine will be most helpful in performing a successful diagnosis

Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data

This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored

Continue by clearing the code and operating the vehicle to see if it returns

This will help to determine whether or not the malfunction is intermittent

After the codes are cleared, test drive the vehicle to see if the code returns

If the code fails to immediately return, you may have an intermittent condition

Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made

Proceed with your diagnostic process by removing and reinstalling the fuel cap and test driving the vehicle (multiple drive cycles may be required to activate a service engine soon lamp) to see if it returns

If other evaporative emission control system codes are present, diagnose and repair them as required

Reset the codes and test-drive the vehicle.
If an evaporative emissions system leak code is present (and the fuel cap is good), visually inspect vacuum and fuel vapor hoses for cracks, splits, kinks, or breakage, and repair as necessary

Inspect the charcoal canister and purge valve for damage or corrosion, replace faulty parts as needed

Start the engine and listen for vacuum leaks near the purge control valve or the hose from the purge valve to the intake

If no leaks are detected, a smoke machine can be very helpful for locating leaks in the extensive network of vacuum and fuel vapor lines that are required for the evaporative emissions control system

Place the vehicle on a lift so that you can observe it from underneath

Start the engine and allow it to enter closed loop operation

Listen carefully to the purge control solenoid

Once the solenoid begins to make a clicking noise, the purge valve should be opened

Place the nozzle of the smoke machine hose into the vacuum supply hose for the purge solenoid and allow the system to fill with smoke

Visually inspect all lines, hoses, and system components for escaping smoke

Pay particular attention to the area around the fuel cap, as faulty gas caps are common

Remember that the charcoal canister usually has a vent which will allow smoke to escape slowly

This is normal

Evaporative emission control system codes that pertain to flow can be best diagnosed beginning with the charcoal canister

A charcoal canister that has become contaminated with liquid can get clogged and restrict purge flow

Check for suction at both sides of the charcoal canister when the purge control solenoid is opened

If there is suction to the canister, it is probably faulty

Remove the canister and shake it, listening for broken or loose particles

Replace the canister as necessary

If the canister proves to be functional, check fuel vapor hoses for kinks from crushing

If the canister and lines appear normal, test the purge control solenoid for proper operation

It should act like a “on/off” valve that is activated by completing a circuit that is normally rated for battery voltage

Check manufacturer’s specs before applying voltage to the solenoid

If the solenoid is faulty, an evaporative emissions control circuit code should also be exhibited

If an evaporative emission control system circuit code is present, inspect electrical connectors and wiring for signs of corrosion or damage and repair as required

If wiring and connectors appear to be operational, unplug the connector from the PCM and perform a resistance check on the purge control solenoid, the system pressure and flow sensors, and system wiring

Compare your findings to manufacturer’s specifications and repair as necessary

Reset the codes and retest the vehicle

Keep in mind, that following repairs, multiple drive cycles may be necessary to verify that the fault condition has been rectified.